In recent years, deterioration of global environment has received attention, inter alia occurrence of global warming has become a serious problem. In order to suppress progress of the global warming, warming preventive measures therefore have been discussed. As one factor of such global warming, CO2 emission is mentioned, for which various specific measures have been proposed to proceed with the suppression of the CO2 emission.
As measures for suppressing the CO2 emission, there has been proposed to take means for preventing the CO2 emission from the beginning other than reducing the emission amount of CO2. For this means, electric power generation is mentioned taking advantage of a reproducible energy such as sunlight, wind power or wave power existing in the natural field, where not only the suppression of the CO2 emission in a currently operating thermal plants but also the enhancement of the electric power generation amount by using such a reproducible energy have been carried out.
However, upon taking advantage of such a reproducible energy, e.g. for acquiring an electric power from sunlight energy, a sunlight electric power generation (solar energy generation) system is required to be set up. This solar energy generation system requires solar batteries for directly converting solar energy to electric power. The solar energy generation system itself provides no CO2 emission, highly contributing to emission constraints, where it is disadvantageous that the solar batteries are still expensive for the solar energy generation system with incurring a high setup cost.
Thus, even though the use of the reproducible energy contributes to the CO2 emission constraints, it is accompanied by not only a high setup cost but also restrictions of setup places.